od [man page] - dump files in octal and other formats
od [OPTION]... [FILE]... od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]] od --traditional [OPTION]... [FILE] [[+]OFFSET[.][b] [+][LABEL][.][b]]
t, --format=TYPE select output format or formats -a same as -t a, select named characters -c same as -t c, select ASCII characters or backslash escapes -x same as -t x2, select hexadecimal 2-byte units -l same as -t dL, select decimal longs
Suppose that we have a file which contains:
$ echo -e "one\ntwo\nthree\nfour\nfive\n\nsix" > file
by default all output from od command comes as octal:
$ od file
Fist column is a octal offset of a file and the following output is a file content in octal representation.With -c option we can instruct od command to represent values in a file as ASCII.
$ od -a file
:[[Image:od02.gif]] To get understanding of what a offset is, we can use wc command to get total number of bytes in the file and that convert it with bc to octal number.
$ wc -c file
$ echo "obase=8; ibase=10; 29;" | bc